Hydraulic servomotor mechanism



o. E. scHuRR HYDRAULIC SERVOMOTOR MECHANISM Original Filed Dec. 21, 1945 Feb. 6, 1951 2 Sheets-Sheet l 6 .8 a A 3. a RR mm a M w a w a J I! Q [E n 3 m a w 9 O 4 O v W.- W 2 F m w O I. N y 9 WM T m n b 7 F u 9 4 w r A F M ATTORNEYS Feb. 6, 1951 o. E. SCHURR HYDRAULIC SERVOMOTOR MECHANISM 21, 1945 2 Sheets-Sheet 2 Original Filed Dec.

ATTORNEYS Patented Feb. 6, 1951 HYDRAULIC SERVOMOTOR MECHANISM Otto E. Schurr, Hamilton, Ohio, assignor to Lima- 7 Hamilton Corporation poration of Virginia Hamilton, Ohio, a cor- Original application December 21, 1945, Serial No.

636,390, now Patent No. 2,527,458, dated October 24, 1950. Divided and this application August 17, 1948, Serial No. 44,681

1 This invention pertains to a hydraulic circuit for machine tools, and is a division of my application Serial No. 636,390, filed December 21, 1945 and now matured as Patent No. 2,527,458, issued October 24, 1950. More particularly, this invention pertains to an improved hydraulic operating and control circuit for the relatively movable members of a machinetool.

One of the objects of this invention is to provide a hydraulic circuit for effecting the relative movement of the work and tool holders of a machine tool in a highly eflicient and accurate manner.

Another object is to provide, in a hydraulic circuit having manually operable servo control means, an arrangement for automatically rendering the manual operating means for the servo control means ineffective when pressure is reduced below a predetermined operating value in thecircuit.

And a further object is to provide a hydraulic circuit having a power driven servo valve means for controlling the movement of a machine tool member which is adapted to automatically disconnect the power drive from the servo valve means when the movement of the machine member is arrested by an external force or fixed abutment.

Further features and advantages of this invention will appear from a detailed description of the drawings in which:

Figure 1 is a diagram showing the application of this novel hydraulic circuit to a machine tool having relatively movable work and tool holding members.

Figure 2 is a diagram showing the application ofthe hydraulic circuit of Figure 1 to a machine tool having a plurality of movable members.

Referring to Figure 1, the novel hydraulic circuit is shown applied to a machine tool having a work holder 5 and a tool holder 6 movable relative thereto. In this particular illustration, the work holder 5 is of the rotary or work spindle type and is driven from a source of power or main drive motor 1 through a suitable mechanical power transmission indicated by'the line 8. The tool holder 6 is actuated by means comprising a fluid pressure cylinder 9 having a piston IE] and piston rod l l appropriately connected to the tool slide or tool holder 6.

Power for actuating the fluid in the hydraulic circuit is derived from a suitable source of power or hydraulic pump motor I2 which is connected through a suitable drive connection and shaft l3 to'a high pressure hydraulic pump 14 and a low 7 Claims. (Cl. 121-45) line pressure hydraulic pump l5. Each of these pumps receives a fluid supply through their respective suctionlines l6 and H from the fluid reservoir I8. It is also within the contemplation of this invention to drive the hydraulic pumps I4 and I5 directly from the main drive motor as indicated by the broken line arrow 19 which represents diagrammatically a suitable power transmission connected to the shaft I3a for driving both of the pumps l4 and I5. In this respect, a separate hy-- draulic drive motor l2 would be dispensed with and there would then be provided an arrange-' ment whereby the main drive motor directly actuated the work spindle 5 and also provided thepower for energizing the hydraulic circuit for operating the tool holder 6.

The high pressure pump I! at all times dis-' charges fluid pressure into the main pressure supply line 20. A branch line 20a. of this main supply line 20 is connected to a suitable pressure relief valve 2| which is in turn connected through the drain line 22 for return of discharged fluid from the valve 2| to the reservoir l8, the purpose of this valve being to limit the maximum pressure which may be developed in the line 20 to safe operating limits.

der 9 for the tool holder 6.

In the servo valve 23 is provided an axially re ciprocatable control plunger 21 having appropriate grooves 21a aligned with the supply line 20; and drain lines 24 so that movement of this valve plunger may reversibly control the direction andalso the rate of flow of fluid to and from the cylinder 9. In conjunction with the valve 23, there is also provided an auxiliary seepage drain line 28 which is arranged to connect with the grooves 29 of the servo valve plunger so as to receive any leakage from each end of the valve plunger during the normal operation of the valve. 1 This supplemental drain or seepage line 28, it is to be noted, is connected to the reservoir for re-'.

turn of seepage fluid independent of the normal main return line 24. In this way, the surge in" the line 24 caused by maximum displacement. ofj the servo, valve plunger 21 during rapid traverse 7 movement of tool holder 6 is not permitted to cause leakage to go past the ends of the valve plunger 21.

The servo valve plunger 21, when displaced slightly from its centralized or stop position for the cylinder 9, effects feeding movements with high fluid pressure in the tool holder 6. Under these conditions of feed movements the high pressure pump l4 transmits fluid at low volume and high pressure through the supply line 20 to the servo valve 23. The high pressure existing in the line 26 at this time is transmitted through a branch line 20b to the pressure chamber 30 of the bypass control valve 3| so as to raise its plunger 32 against the compression spring 33 connecting the chamber 34 with the chamber 35. This allows discharge from the low pressure pump l at a predetermined pressure, determined by the spring 33 opposing the pressure in the chamber 3|], to pass through the lines 36 and 36a, to enter the drain line 31 for return of fluid to the reservoir l8. Under normal feeding conditions the low pressure pump pressure supply is thus bypassed so that it merely circulates fluid from the line I! to the line 36, through the valve 3| to the drain line 31.

Should it be desired to efiect rapid traverse movements in the tool holder '6, the valve plunger 21 of the servo valve 23is displaced a relatively large amount from its neutral or stop position. This provides a large discharge opening from the cylinder 9 to the main drain line 24 and correspondingly decreases the pressure required to move its piston H) by pressure supplied by the line 20. Pressure thus drops in the line during rapid traverse movements which in turn, through the branch line 2%, decreases pressure in the pressure chamber 36 of the bypass valve 3|. The plunger 32 is thus forced downwardly by the greater pressure of the spring 33,

closing discharge from the, low pressure pump l5 through the lines 36 and 36a into the drain 1ine3l. At the same time, the pressure drop in the line 20 decreases below the pressure in the line 36 as normally maintained by the spring 33 opposing the pressure in the chamber acting on the plunger 32 so that the check valve 38 opens so that fluid pressure from the low pressure pump I5 passes through the line 36 and the line 361) through the check valve 38 into the branch line 200 of the main supply line 20. In this way, the low pressure pump |5 automatically supplements the flow provided by the high pressure pump M to provide an additional low pressure large volume supply in the line 20 to efiect the desired rapid traverse movement in the tool holder 6. Thus it can be seen that the servo control valve 23 is arranged to be supplied by fluid pressure from a dual pump and that the single supply line connected to the servo valve is capable of providing any desired feed or rapid traverse movement for the tool slide 'actuating cylinder by merely effecting the desired amount of displacement of the servo valve plunger.

The servo valve plunger 21 i preferably at:- tuated by a servo valve screw 39 which is attached to the valve plunger 21 and arranged for axial movement to reciprocate the valve plunger but provided with any suitable means to maintain it in nonrotatable condition. Preferably,

the servo valve 23 is mounted rigidly on the ma chine frame while an actuating 'nut '40 is journaled against axial displacement in a suitable bearing 4| fixed in the actuable member, tool slide, or tool holder 6. By rotating the nut 46 the screw 39 and the connected valve plunger 21 are moved relative to the valve 23 momentarily during the initial adjustment of the valve. The rotation of the nut 40 also re-adjusts the position of the valve plunger 21 and crew 39 relative to the tool carrier 6 to in this way effect the relative servo control movement of tool slide as in a conventional manner for such servo valve mechanism.

The nut 40 may be rotated manually by means of a hand wheel 42 which is journaled for axial sliding movement on a suitable bearing 43 on the shaft 44. This shaft is journaled on bearing's 45 preferably on the tool carrier 6. The shaft 4 1 is provided with a bevel gear 66 which in turn meshe with a mating bevel gear 41 on a shaft 48 which in turn has a bevel gear 49 adapted to engage a bevel gear 50 formed on the servo screw nut 46. The hand wheel is provided with clutch teeth 5| which are adapted to engage mating clutch teeth 52 on a clutch member 53 fixed to the shaft 44 by a pin 54. A compression spring 55 normally holds the hand wheel 42 in disengaged position of the clutch teeth 5| and 52. When the hand wheel 42 is pushed inwardly to engage these clutch teeth and rotated, the nut 40 may thus be relatively adjusted to move the screw 39 and valve Plunger 27 relative to the tool slide 6 and valve 23 to effect the servo control.

Means are provided .ior automatically rendering the hand wheel ineffective to adjust the servo valve when the fluid pressure pumps I4 and I5 are not operating or the pressure in the hydraulic circuit has dropped below a predetermined safe operating level. A lockout plunger 56 is arranged to be moved between the clutch members 5| and 52 by a suitable compression spring 51 when fluid pressure in the line 20 and branch line 2011 drops below a predetermined safe operating level or drops to zero when the pumps I4 and I5 are not being driven. Thus the hand wheel 42 cannot be moved inwardly to engage the clutch teeth 5| and 52 under these conditions. As soon as the pumps l4 and I5 are started so that proper operating pressure exists in the main line 20, pressure in the branch line 20d enters in the pressure chamber 58 behind the lockout plunger 56 to raise its piston 59 against the spring 51, thus. withdrawing the plunger 56 and permitting engagement of the hand wheel clutch members 5| and 52. The purpose of this arrangement is to prevent re-adjusting the servo valve when the machine is shut down, particularly to a wide open position, and then energizing the hydraulic pump .1 motor |2. This would cause a surge of pressure in the tool slide cylinder which in turn causes the tool slide to jump ahead and thereby move the servo valve beyond its other position and damage the valve or otherwise position the servo valve plunger in an inoperative location. Thus, with this arrangement, the tool slides and servo valves cannot be adjusted by the hand wheels so long as the hydraulic system is inoperative.

The servo screw nut 4|] may also be reversibly driven by power received from the main drive motor and transmission indicated by the line 3 through a rate changer 66 including a suitablefeed reverser which effects difierent rates of variable speed output through'suitable transmission mechanism indicated by the line 6| which is connected-to one member 62 of a-feed and rapid traverse clutch. The other member of this clutch is connected to a reversible rapid traverse driving power source such as a rapid traverse electric motor 64 connected through a suitable transmission indicated by the line 65 to the member 63. The clutch member 63 may also, if desired, be driven by a connection indicated by the broken arrow 66 directly from the main drive motor and transmission 8, in which case the separate rapid traverse motor 64 would not be utilized, while a suitable reverser 66a is provided for reversing the rapid traverse drive.

A suitable clutch selector member 61 is alternately connectable to the member 62 for feed movements or other member 63 for rapid traverse movements to transmit power from the member 67 through a suitable power transmission indicated by the line 68 and through a magnetic clutch 69 to the servo screw nut 46. Thus, in this arrangement, the servo screw nut may be oper ated at variable feeding speeds by the ratechanger 60 or at rapid traverse rate, either from the independent electric rapid traverse motor 64 or from the main drive motor 1 through the drive connection 86665.

In certain types of machine tools, itis desirable;

and essential to move the tool feeding device 6, having an integral lug 10, up against a fixed abutment ll carried in the machine frame F so as to positively stop the tool slide in a predetermined accurate position. In a servo valve control mechanism which is power driven as above described, when the tool slide reaches and enof the servo valve after a predetermined amount of adjustment has taken place in the servo valve plunger upon engagement of the tool slide with the fixed abutment.

As an example of a preferred arrangement to accomplish this result, there is provided a'limit switch 12 carried on the machine frame F which is operatively electrically connected through suitiable leads l3 and electrical apparatus with the magnetic clutch 69.

cam surfaces 15 and 16 which engage and operate the control arm 11 of the limit switch 12 when the relative adjustment of the screw 39 and servo plunger 2'! exceeds a predetermined value either side of the neutral or stop position of the valve. Thus, as the tool slide engages the abutment" and its motion is definitely stopped; the servo screw continues to be adjusted by the power drive above described until the relative movement of the screw 39 causes either surface 15 or 16 to engage the limit switch 12. The magnetic clutch 69 is thus de-energized to automatically disconnect all power drive to the servo screw nut and bring the servo valve to a stop in an opened position.

In order to reverse or back the tool slide away from the fixed abutment, the operator engages the manual control hand wheel 42 to connect the clutch members 59 and 52 and rotates the On the servo screw 39' fixed an actuating cam I4 having appropriate hand wheel in the reverse direction until the 6 magnetic clutch 69 is re-energized so as to again complete the power drive connection to the servo screw nut. The power feed or rapid traverse drive may then be operated in the reverse direction to efiect the power control of the servo valve for automatically returning the tool holder away from the abutment to initial cutting position for the beginning of another work cycle. I

In Figure 2 is shown the application of these hydraulic circuit principles to a machine tool having a plurality of actuable members or tool slides or holders 6, 6a, 6b, and 60, each appropriately mounted on the machine frame and connected to be moved by the respective fluid pressure cylinders 9, 9a, 9b, and 9c. cylinder is provided with appropriate pistons l0 and piston rods ll connected to the tool slides or holders 6 to Sc inclusive. Each of the cylinders 9 to Sc inclusive is controlled by appropriate servo valves 23, 23a, 23b, and 23c in the manner shown in Figure 1. The cylinders are each connected by suitable connecting lines 25 and 26, 25a and 26a, 25b and 26b, and 250 and 260, re-' spectively to the, servo valves 23 to 230 inclusive. Gravity balancing valves 25y are connected in lines 2511. and 250 to ofiset the downward weight of the tool bars 6a and by providing free flow from the servo valves 23a and 230 to the bottom of the cylinders 9a and 90, but providing a restricted flow out of the bottom of these cylinders to balance the normal downward movement of' the tool bars. This allows the same effective servo control for both up and down movements of the bars. Each of these servo valves may be controlled by power applied to the servo screws 39, 39a, 39b, and 39c through the respective nuts 49, 40a, 49b, and 400 as in Figure 1, or manual control may be efi'ected by the hand wheels 42, 42a, 42b, and 420 as in Figure l.

In connection withslides 6 and 6b, the hand wheel actuating mechanism for adjusting the threaded rods connected with the servo valvemembers are carried by the slides so as to move therewith. In this manner the gearing connecting the hand wheels with the threaded rods is always engaged and the rods can be manually adjusted at any time that itis possible to engage the clutches associated with the hand wheels.

The hand wheel mechanism associated with the slides 6a and 60, on the other hand, are stationary as are housings of the servo valves 23a and 230. However, the spur gearing 49, 460 for servo valve 230 and 49, 46a for servovalve 23a permit a certain amount of reciprocation 0f the threaded valve adjusting rods relative to 'the hand wheel structures. Inasmuch as the valves are normally maintained very close to their cen-ffl, ter position, the said threaded rods will at all 1 times be drivingly engaged with the hand wheel mechanism and can be adjusted thereby at any time the clutches of the hand wheels can be engaged.

l4l5 and I4al5a. Each of these dual pumps l4--l5 and l4a-l5a is driven from a common.

source of power or electric motor In and receive a supply of fluid through the suction lines 18. The dual pump I4-l5 transmits pressure through a single pressure supply line 19 which is connected to the servo valves '23 and 23a while the dual pump l4a,l5a transmits pressure through another single pressure supply line tothe servo valves 23b and 230. This system is b Each of theseso arranged that one or the other or both of the dual pumps may be operated to supply pressure to the respective lines 19 and 89. This may be accomplished by providing bypass valves 8| and 82 forconnecting the discharge from the respective pumps back to the reservoir l8 when it is desired to cut out one or the other of these pumps when the motor lZa is energized. Thus, in this system some of the tool slides maybe rendered inoperative even though the hydraulic pump motor no is energized.

It is to be further noted that individual lookout plungers 56 are provided for each of the hand wheel controls in a manner as shown in Figure l. and appropriately connected to the corresponding pressure supply lines for the associated servo valve of each particular'hand wheel. In other words, the hand wheels 42 and 42a are provided with the lookout plungers 56 and 58a, these lookout plungers being operatively hydraulically con-' nected by suitable lines 19a with the pressure supply line 19 from the dual pump l4l5. The hand wheels 42b and 420 are provided with the lockout plungers 56b and 560 connected through the branch lines 80a with the pressure supply line 80 from the other dual pump i4a-l5a. Thus, each of the tool slides or carriers 5, 9a, 6a, or 60 may be operated independently of one another with this hydraulic circuit arrangement with all of the various desired servo control functions for the group of tool slides rendered manually operative by the readily available hand wheels 42, 42a, 42b, and 420,

Each of the servo control valves is connected to a main drain or return line 9!, as in Figure l, for the return of fluid to the reservoir [8, and it is to be noted that each of the actuating cylinders for the tool slides is provided with bleeder-lines 92 having air bleeder choke coils 920: connected through an independent circuit indicated generally at 92 for return of seepage and bleeder discharge from the cylinders and serve valves to the fluid reservoir or to the main drain line at a and that such mechanical arrangements and,

commercial adaptations as fall within the scope of the appendantclaims are intended to be hi cluded herein.

Iclaim: i 1. .In a hydraulic servomotor mechanism. for

a fluid motor having a relatively reciprocable pise' having a connection with the other of said piston and cylinder for movement in unison therewith, said valve member having a neutral position for interrupting fluid flow to said cylinder, and being movable in opposite directions from its neutralposition to direct fluid to one end or the other of said cylinder, said cnnection being adjustable in length, actuating means operable for efieGting adjustment of said connection to move said valve member from its neutral position thereby to bring about a supply of fluid to said cylinder to move the piston and cylinder relatively in a direction to return said valve member toward its neutral.

position, and means responsive to a predetermovement of said valve member in said casing. in either direction from its neutral position for mined movement of said valve member from its neutral position in said casing in either direction for making said actuating means ineffective.

' 2. In a hydraulic servomotor mechanism for? unison therewith, said valve member having a;-

neutral position in said casing for interrupting fluid flow to said cylinder and being movable in opposite directions from the neutral position for reversibly directing fluid to said cylinder, said connection being adjustable in length, actuating means operable for adjusting the length of said connection for shiftin said valve member in said casing, whereby fluidis directed to the cylinder; to move the piston in a direction to return the valve member to its neutral position, and means responsiveto a predetermined amount of move ment of said valve member from its neutral position in said casing in either direction for dis-.

connecting said, actuating means from said con nection.

3. In a hydraulic servomotor mechanism a fluid motor having a piston and cylinder, a

servo valve hydraulically connected with said cyl inder comprising a casing rigid with said cylinder and a valve member reciprocable in the casing and having a screw threaded connection, with said piston, said Valve member being movable; in the casing from a neutral position where fluid flow to the cylinder is interrupted in opposite directions for reversibly directing fluid to said cylinder, actuatin means connected for adjusting said screw-threaded connection between said valve member and piston, and means responsive to a predetermined movement of said valve men her in said casing in either direction from the' said neutral position for automatically disconmeeting said actuating means from said threaded connection. a. In a s-ervomotor mechanism for a fluid motor having a piston and cylinder, a servo valve comprising a casing rigid with said cylinder and hydraulically connected therewith, a v 1 'i ber reciprocable in said casing for reversibly con: trolling fluid flow to said cylinder, a threaded rod on a d al e m mbe a nut n en nt ith said rod and movable with said piston whereby said piston and valve member normally move in unison but said nut can be rotated for shiftingsaid valve member in the ca n thereby 0 br n about the actuation oi said piston, actuating means li nlld ted with said n t for selectively driving it in one direction or the other, and,

m an responsi e to a pr det amount o disconnecting said actuating means from said nut,

5, In a hydraulic ,servomotor mechanism tor a fluid mot r avin a piston and cylinder, a

servo valve having a casing hydraulically con;

ected wit said ylind n rigid therewith an also having avalve member reciprocable in .theing or reversibly controlling the fluid supply to said cylinder, a rod on said valve member have;

ns t ad ther on, a nu ng i g said ad and mounted or movement with said pistonv whereby said piston and valve member normally move in unison, actuating means connected with said nut for selectively driving it in one direction or the other, thereby to adjust said valve memher in its casing to bring about the actuation of said piston, abutment means for halting said piston in a predetermined position, and means responsive to continued movement of said valve member after said piston has been halted by the said abutment as brought about by the driving of said nut for efiecting disengagement of the said actuating means from said nut.

6. In a servo motor mechanism for a fluid motor having a piston and cylinder, a servo valve comprising a casing rigid with said cylinder and hydraulically connected therewith, a valve member reciprocable in said casing for reversibly controlling fluid flow to said cylinder, a threaded rod on said valve member, a nut in engagement with said rod and movable with said piston whereby said piston and valve member normally move in unison but said nut can be rotated for shifting said valve member in the casing, thereby to bring about the actuation of said piston, actuating means connected with said nut for selectively driving it in one direction or the other, means responsive to a predetermined amount of movement of said valve member in said casing in either direction from its neutral position for disconnecting said actuating means from said nut, and manually operated means selectively oper able for actuating said nut independently of said actuating means.

7. In a servomotor mechanism for a fluid motor having a piston and cylinder, a servo valve comprising a casing rigid with said cylinder and hydraulically connected therewith, a valve member reciprocable in said casing for reversibly controlling fluid flow to said cylinder, a threaded rod on said valve member, a nut in engagement with said rod and movable with said piston whereby said piston and valve member normally move in unison but said nut can be rotated"for shifting said valve member in the casing, thereby to bring about the actuation of said piston, actuating means connected with said nutf foi' selectively driving it in one direction or thepther, means responsive to a predetermined an; int of movement of said valve member in said sing in either direction from its neutral position-for disconnecting said actuating means from sa gut, manually operated means selectively oper for actuating said nut independently of: 1d actuating means, said manually operable means bein normally disengaged from said nut being manually engageable therewith, and means responsive to the pressure of the actuatingfluid controlled by said servo valve for preventing manual engagement of said manually operable means whenever the said pressure is below a predetermined amount.

OTTO E. SCHURR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATEENTS 

